HostingRails.com

Hi - Yes, Using mongrel cluster will speed up your apps. When you have a single Mongrel instance for you apps - then it will handle the http requests to your site serially. But when you have Mongrel cluster running - the http requests to your site can be handled concurrently by it.

So if heavy traffic to your site, it would be better having mongrel cluster for your apps. And usually for small to medium-sized applications use less than 50 MB per Mongrel instance. So you need to have 50MB of dedicated memory for running a single instance. You can refer this link to get a better idea about the number of mongrel instance you need to run.

"But when you have Mongrel cluster running - the http requests to your site can be handled concurrently by it."

does that mean a site on a mongrel cluster can handle more than 1 request at a given time? so if my site is mostly dynamic where some requests can only be handled at a rate of 3-6 requests per second, mongrel cluster could handle more than the 3-6 requests per seconds? like if i had 12 users doing the same action at a given time?

Hi there - yes, you are thinking about this correctly.  Mongrel will queue up requests but can only serve one at a time, which is why its usually clustered and load balanced.  

"can cache_fu memcached be installed on my account? just wondering in case my site becomes popular."

I've been looking into memcached recently and using in on a non HR hosted project. It seems a great way to speed up pages of sites of mine that are generating a lot of database traffic and template processing.

@ the HR team: I looked around but found no mention of running a memcached server on a HR account. Is it possible? what would be the procedure for setting that up?

You'll need a VPS or dedicated plan to setup a memcached environment.  It is too resource intensive for everyone on a shared server to use.